The present invention relates to a combination process for producing high octane gasoline or gasoline blending components and middle distillates for fuels or blending components from a light boiling range hydrocarbon charge stock. There are many prior art processes dealing with methods of upgrading gasoline or converting higher boiling point fractions to obtain high octane gasoline. U.S. Pat. Nos. 3,658,690 and 3,649,520 show traditional processing elements for improving the octane of a gasoline boiling range feedstock via reforming, aromatic separation and isomerization. Other processes for converting straight run gasoline and kerosene boiling fractions into improved octane motor fuels also include catalytic cracking and alkylation steps. U.S. Pat. Nos. 3,787,314 and 3,758,401 are representative of such schemes. However, the major objective of these inventions is the production of gasoline without regard to the yield of other middle products. As indicated by U.S. Pat. Nos. 3,726,789 and 3,756,940, it is typically taught to crack or reform paraffinic components having 7 or more carbon atoms into higher octane isomers or aromatics. The conversion of paraffinic components to higher density aromatics results in a volumetric shrinkage of product. The problem of volumetric shrinkage of paraffin components is addressed in U.S. Pat. Nos. 3,788,975 and 3,650,943. Nevertheless the two referenced patents still teach the combination of refining aromatic extraction and paraffin cracking only in relation to the production of unleaded gasoline. Thus the emphasis of the prior art has been the maximization of octane for gasoline products when processing a naphtha boiling range feed with little attention given to the total liquid product yield.
In regard to middle distillate production the combination of reforming, aromatic extraction, cracking, and alkylation have been used in the production of jet fuels as demonstrated by U.S. Pat. No. 3,533,938. However, these processing steps were arranged to obtain such fuels from heavy hydrocarbon feeds and not to maximize the liquid volume of gasoline and middle distillate product. Of course, methods of increasing the middle distillate to gasoline ratio of products obtained from heavy hydrocarbon feeds as exemplified by U.S. Pat. No. 3,349,023 are known. Nevertheless, such processing schemes do not demonstrate the method of using hydrocarbon components of lighter boiling fractions to optimum advantage.
There is an increasing demand for methods of processing naptha boiling range fractions in a manner which will produce high cetane middle distillates along with high octane gasoline components.
Concentration on increasing octane for gasoline products is of course a direct result of the demand for unleaded gasoline and an increasing market for premium grade unleaded fuel. In a conventional reforming scheme for upgrading octane the C.sub.7 -C.sub.10 paraffins are typically converted in part to aromatics and hydrocracked to some extent into lighter gasoline products and fuel gas. However, neither of these reactions takes full yield and octane advantage of the components since the aromatization of the paraffins into higher density components results in a large volumetric shrinkage while the paraffin gasoline constituents are poor in octane number.
The failure to optimize the use of light hydrocarbon components will become less tolerable with the expected increase in the distillate to gasoline ratio for petroleum motor fuel products. Although the automotive diesel market has not risen according to predictions, the decreased gasoline consumption of newer automobiles and the rising demand for jet fuel should still shift the product ratio over to increased distillate production. As a result, it will become desirable to increase total product yield of gasoline and distillate in addition to upgrading the octane number of the gasoline fraction and cetane number of the distillate.